An apparatus for magnifying and projecting images of a liquid crystal panel by using a light source such as metal halide lamp has been hitherto known. In such liquid crystal projection apparatuses, the light generated from the lamp light source is focused on the liquid crystal panel through an optical system of mirrors and others, and displayed on the screen through a projection lens. Recently, a liquid crystal projection apparatus of a high luminance type is available so that images projected on a wide screen can be seen even in a bright room. The liquid crystal projection apparatus of high luminance type comprises an optical system having a high output lamp, small-sized light emitting device, and an improved light utilization rate. FIG. 5 shows an example of an optical system of such liquid crystal projection apparatus. In order to further enhance the brightness of the image, a liquid crystal projection apparatus having two or more lamps as the light source is also developed. The liquid crystal projection apparatus of the invention has two or more lamps as the light source. FIGS. 6(a) and (b) show the two-lamp optical system of the liquid crystal projection apparatus disclosed in Japanese Laid-open Patent No. 5-29320. FIG. 7 shows the two-lamp optical system of the liquid crystal projection apparatus disclosed in Japanese Laid-open Patent No. 5-49569. As shown in FIG. 7, a light emitting tube 20 is fixed near the focus of a reflecting mirror 21 of an elliptical or parabolic surface, and the light from the light emitting tube passes through the focusing system parts consisting of first lens array 24, second lens array 25, and field lens 23, and illuminates a liquid crystal panel 26. The first lens array 24 and second lens array 25 have an integrator function for illuminating the screen uniformly. The image from the liquid crystal panel 26 is synthesized into a color image by a cross prism, and is magnified and projected on the screen by a projection lens 27. The two-lamp optical system is capable of obtaining a bright image, but it has its own problem in cooling of two lamps. FIG. 7 shows an example of cooling of two lamps. An axial flow fan 30 cools the lamps from behind in order to keep the temperature below about 950.degree. C. in the upper part of the light emitting tube 20, and below 350.degree. C. in the seal part. However, the case of two-lamp system, for example, in the case of lamps in a structure enclosed by the reflecting mirrors and front glass as in the super-high pressure mercury lamps, if there is an air vent near the front glass of the lamp, it is difficult to limit temperature rise of lamps by cooling from behind by the axial flow fan 30. It is also difficult to cool the two lamps in the same state. Cooling of two lamps and cooling of the entire apparatus are more difficult as the size of the apparatus is more compact. To solve these problems, it is hence an object of the invention to present a liquid crystal projection apparatus having two or more lamps capable of keeping the temperature in the apparatus within a specified temperature and cooling two or more lamps in a same state. It is also an object of the invention to present a lamp capable of keeping the temperature of the light emitting tube and other parts in the lamp within a specified temperature, by forming an air passage in the lamp.